KVM: selftests: complete IO before migrating guest state
authorSean Christopherson <sean.j.christopherson@intel.com>
Wed, 13 Mar 2019 23:49:31 +0000 (16:49 -0700)
committerPaolo Bonzini <pbonzini@redhat.com>
Thu, 28 Mar 2019 16:29:09 +0000 (17:29 +0100)
commit0f73bbc851ed32d22bbd86be09e0365c460bcd2e
treeea284f7f136478bbbef72f205ee29944a761a859
parentffac839d040619847217647434b2b02469926871
KVM: selftests: complete IO before migrating guest state

Documentation/virtual/kvm/api.txt states:

  NOTE: For KVM_EXIT_IO, KVM_EXIT_MMIO, KVM_EXIT_OSI, KVM_EXIT_PAPR and
        KVM_EXIT_EPR the corresponding operations are complete (and guest
        state is consistent) only after userspace has re-entered the
        kernel with KVM_RUN.  The kernel side will first finish incomplete
        operations and then check for pending signals.  Userspace can
        re-enter the guest with an unmasked signal pending to complete
        pending operations.

Because guest state may be inconsistent, starting state migration after
an IO exit without first completing IO may result in test failures, e.g.
a proposed change to KVM's handling of %rip in its fast PIO handling[1]
will cause the new VM, i.e. the post-migration VM, to have its %rip set
to the IN instruction that triggered KVM_EXIT_IO, leading to a test
assertion due to a stage mismatch.

For simplicitly, require KVM_CAP_IMMEDIATE_EXIT to complete IO and skip
the test if it's not available.  The addition of KVM_CAP_IMMEDIATE_EXIT
predates the state selftest by more than a year.

[1] https://patchwork.kernel.org/patch/10848545/

Fixes: fa3899add1056 ("kvm: selftests: add basic test for state save and restore")
Reported-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
tools/testing/selftests/kvm/include/kvm_util.h
tools/testing/selftests/kvm/lib/kvm_util.c
tools/testing/selftests/kvm/x86_64/state_test.c